Method and system for maximizing data throughput rate in a power line communications system by modifying payload symbol length

ABSTRACT

Data throughput rate in a power line communications (“PLC”) system is controlled by generating PLC carrier signals in accordance with a PLC signal frame structure containing payload symbols where the payload symbol length is selected based on at least one of a PLC system channel quality and node configuration data. The selected payload symbol length determines the processing operations that a source PLC transceiver performs for generating PLC signals or that a destination PLC transceiver performs for extracting information content from received PLC signals. The payload symbol lengths can be selected to maximize the data throughput rate while maintaining compatibility with prior art PLC system protocols and standards that require a PLC signal frame structure and its payload portion to have fixed, predetermined lengths.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/404,360 filed Aug. 19, 2002, which is incorporated by referenceherein.

FIELD OF THE INVENTION

This invention relates to the field of communications over conventionalelectric power conveying media, and more particularly, to improving datathroughput rate in a power line communications (“PLC”) system bymodifying the length of payload symbols included in a PLC signal framestructure in view of PLC system channel quality information.

BACKGROUND OF THE INVENTION

In a PLC system, information is conveyed over conventional power linemedia on PLC data carrier signals. The PLC system includes PLCtransceivers that operate in accordance with predetermined PLC protocolsand standards. The protocols and standards are formulated in view of theprocessing capabilities of the PLC transceiver equipment and theexpected PLC signal transmission characteristics of the PLC system. Theprotocols and standards, for example, define the spectrum of frequenciesused for PLC signal transmissions and how information content andassociated control data are carried on PLC signals. The arrangement ofinformation content and overhead data within a PLC signal is typicallyreferred to as a frame structure. The frame structure establishes thesequence that PLC signals containing overhead and information contentdata are generated for transmission over the PLC system.

When many of the prior art PLC systems, such as orthogonal frequencydivision multiplexing (“OFDM”) PLC systems, were designed, the lack orlimited availability of high speed processing technology dictated thecharacteristics of the PLC signal frame structure. The current andwidely used PLC signal frame structure, which is substantially the sameas the frame structure adopted in early prior art PLC systems, includesa payload portion interposed between start and end delimiters. SeeGardner, S. et al., “HomePlug Standard Bring Networking to theHome”http://www.commsdesign.com/main/2001/12/0012feat5.htm, Dec. 12,2000, incorporated by reference herein. The start and end delimitersinclude communications overhead data, such as a preamble, destinationaddress, source address, network protocol type and frame check (errorcorrection), which a destination PLC transceiver requires for extractinginformation content and other control data from the PLC signalstransmitted by a source PLC transceiver. The payload portion contains aplurality of payload symbols. Each of the payload symbols represents oneor more information content data modulated PLC carriers which are to begenerated at and transmitted from the PLC transceiver.

Based on the prior art PLC system design, each of the payload symbolshas a fixed, predetermined length determined by the fixed, predeterminedlength of the payload portion and a portion of the fixed length of eachof the payload symbols is allocated to a cyclic prefix. See Gardner. Thecyclic prefix is essentially a replication of the last few microsecondsof the payload symbol. As well known in the art, the cyclic prefixlength is included in the payload symbol to avoid the adverse effects ofintersymbol interference, which may occur because network segments inthe PLC system can cause different PLC carriers to experience differentrespective transmission delays. If the cyclic prefix is not included ina payload symbol, some of the data samples obtained when converting thereceived time domain PLC carrier waveforms generated for a subjectpayload symbol to frequency domain data could represent energyassociated with PLC carriers generated for a payload symbol thatprecedes or follows the subject payload symbol in a frame structure.Thus, in PLC system design, the length of the cyclic prefix in a payloadsymbol usually is set equal to the expected worst case delay variationacross the PLC frequency spectrum for the PLC system. This cyclic prefixlength ensures that conversion of the PLC carrier waveform intofrequency domain data begins at the portion of the PLC carrier waveformfollowing the end of the cyclic prefix, thereby providing that thefrequency domain data obtained based on the received PLC carrierwaveforms generated for the subject payload symbol is not degraded byany of the PLC carriers generated for the payload symbols preceding orfollowing the subject payload symbol.

It is further noted that the prior art fixed length payload symbolrequirement provides that, for each payload symbol, time domain PLCsignals having only predetermined carrier frequencies can be generated.The predetermined carrier frequencies for the PLC signals are within apredetermined PLC frequency spectrum and, in addition, only selectedmodulation methods can be applied for modulating data onto the PLCcarrier signals. See, for example, U.S. Pat. No. 6,523,256, incorporatedby reference, for a description of modulation methods that can be usedin connection with PLC carriers generated for payload symbols. Alsoaccording to the prior art PLC system design, a single modulation methodmust be used in connection with each of the PLC carriers generated for apayload symbol. As is well known in the art, the modulation method,which establishes predetermined orders of modulation that can be used tomodulate PLC carriers, determines the amount of data that a PLC carriercan carry.

Although the prior art PLC signal frame structure design limits themaximum available data throughput rate in a PLC system, this result wastolerated or required in view of the limitations of the data and signalprocessing technologies available in the prior art and to ensurereliable and accurate transfer of information content using PLC signals.

Since the development of the prior art PLC frame structure design, whichcontinues to be used in a vast majority of current PLC systems,advanced, higher speed signal and data processing technologies havebecome available and cost effective for use in PLC transceiverequipment. PLC systems and PLC equipment, however, continue to utilizethe prior art PLC signal frame structure design, which in manycircumstances unnecessarily limits the maximum available data throughputrate for the PLC system.

Therefore, a need exists for a system and method for maximizing datathroughput rate in a PLC system in view of available higher speed dataprocessing technologies and while also permitting that existing PLCtransceiver equipment can continue to be used without difficult orcostly modifications.

SUMMARY OF THE INVENTION

In accordance with the present invention, the data throughput rateassociated with PLC signal transmission in a PLC system is maximized byselectively controlling the length of payload symbols included in a PLCsignal frame structure from which PLC data signal carriers aregenerated. The selected payload symbol length is computed based on PLCsystem signal transmission performance channel quality data obtained inreal time, based on non-real time processing configuration data (“nodeconfiguration data”) obtained from PLC signals transmitted over the PLCsystem to, or pre-programmed at, PLC transceiver equipment or based on acombination of the channel quality data and the node configuration data.

In a preferred embodiment of the present invention, payload symbollength is modified while providing that PLC signal processing otherwisefollows prior art PLC frame structure (“legacy”) design requirements,i.e., each of the frame structure and the payload portion of the framestructure has a fixed, predetermined length that cannot be changed. Whenthe PLC signal transmission characteristics (“channel quality”) for thePLC system is at a sufficiently high level, a length is selected for apayload symbol that exceeds the fixed payload symbol length of thelegacy design. By increasing the length of the payload symbols in thepayload portion, while maintaining the payload portion at the fixedlegacy length, the sum of the lengths of cyclic prefixes, which areincluded within the respective payload symbols and occupy portions ofthe symbol lengths, in the frame structure is reduced. Each of theincreased length payload symbols provides that a PLC transceivergenerates and transmits a greater number of PLC carrier signalscontaining information content, during the time interval of the framestructure corresponding to the increased length symbol, than that whichwould be generated and transmitted based on a legacy payload symbolhaving a shorter length. In other words, the increased length payloadsymbols in the payload portion provide that more data can be transmittedin a PLC signal transmission than that transmitted for a legacy PLCsignal transmission for the time interval corresponding to the length ofthe PLC signal frame structure, thereby increasing the data throughputrate for the PLC system.

In a preferred embodiment of the present invention, a PLC transceiverwithin a PLC system generates a PLC signal frame structure includingpayload symbols each having a same selected length, where the payloadsymbol length is selected for maximizing the data throughput rate in thePLC system in view of PLC system channel quality data and the nodeconfiguration data. The PLC transceiver itself computes channel quality,or receives node configuration data on PLC signals transmitted fromanother PLC transceiver source. The PLC transceiver processes thechannel quality or the node configuration data, or both of the channelquality and node configuration data, to determine the longest possiblepayload symbol length likely to ensure accurate reproduction ofinformation content at a destination PLC transceiver based ontransmission of a PLC signal, which is generated based on the selectedpayload symbol length, over the PLC system.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparentfrom the following detailed description of the presently preferredembodiments, which description should be considered in conjunction withthe accompanying drawings in which:

FIG. 1 is an exemplary power line distribution system for high speeddata communications.

FIG. 2 is a block diagram of a preferred OFDM PLC transceiver inaccordance with the present invention.

FIG. 3 is an illustration of an exemplary prior art PLC signal framestructure.

FIG. 4 is a high level flow diagram of a process for maximizing datathroughput rate by selecting a payload symbol length in accordance withthe present invention.

FIG. 5 is an illustration of an arrangement of payload symbols in apayload portion of an exemplary prior art PLC signal frame structure.

FIG. 6 is an illustration of an arrangement of payload symbols in apayload portion of an exemplary prior art PLC signal frame structuregenerated in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention of selectively controlling the length of a payloadsymbol of a PLC signal frame structure is explained in connection withoperations performed at a PLC transceiver of an OFDM PLC system which isdesigned for conveying PLC data signals over conventional utilityelectrical power media. It is to be understood, however, that thepresent invention can be applied to OFDM based or other communicationsystems operating on other types of wired or wireless media.

FIG. 1 illustrates an exemplary, prior art electric power distributionand high speed data communications system 10, which includes bothutility electric power distribution and in premise power distributioncapabilities and over which PLC data signals generated in accordancewith the present invention can be conveyed. Referring to FIG. 1, thesystem 10 includes a standard medium power substation 12 coupling a highvoltage power line 14 to a common medium voltage power line and datadistribution access network 16 via a switch cabinet 15. The network 16is typically configured in a loop, several miles in length, andpositioned in proximity to low voltage access points 20A-20H, which canbe homes, businesses or other entities. Step down transformers 18 couplethe network 16 to low voltage access lines 22, which are at 110-240 V ACand extend to the respective low voltage access points 20. It is to beunderstood that the network 16 can include power and communications datadistribution elements located above as well as below ground. Thus, thenetwork 16 forms a wide area data network (“WAN”) for datacommunications and supplies electricity to the low voltage access points20. Electric power meters 24 couple respective ends of the low voltagelines 22 to conventional in-home or in-building electricity distributionnetworks 26, which are contained within the low voltage access points20. As well known in the art, electronic appliances 21 include PLCtransceivers (not shown) having PLC data signal processing capabilitiesand which can be connected to one another to form a local access network(“LAN”) for data communications within a home, business or otherenvironment, are coupled to the network 26 within an access point 20.Also as well known in the art, PLC data signals can be used to transmithigh speed data across all segments of the network 10.

In accordance with the present invention, a PLC transceiver selectivelycontrols the length of the payload symbols in a PLC frame structure fromwhich PLC signals are generated, based on the results of an evaluationof PLC system channel quality data, processing configuration data (“nodeconfiguration data”) obtained from PLC signals transmitted over the PLCsystem to, or pre-programmed at, the PLC transceiver, or a combinationof the channel quality data and the node configuration data, to maximizethe data throughput rate and, therefore, increase the efficiency ofutilization of the PLC system as a channel for transferringcommunications data. Referring to FIG. 1, the inventive PLC transceivercan be installed in all segments of the PLC system 10 where a higherdata throughput rate is desired. For example, each of a first electronicappliance 21 coupled to the network 26 within a first access point 20and a second electronic appliance 21 coupled to the electricdistribution network (not shown) within a second access point 20 cancontain the inventive PLC transceiver for maximizing the data throughputrate for PLC signal transmission between the first and second accesspoints 20. Also for example, in the PLC system 10, each of theelectronic appliances 21A and electronic appliance 21D is coupled at adifferent point to the network 26 within the access point 20A and cancontain the inventive PLC transceiver for maximizing the data throughputrate for PLC signal transmission between the two coupled points of thenetwork 26.

FIG. 2 is a preferred embodiment of an OFDM PLC transceiver 50 thatestablishes the physical connection and electronic signal link betweenthe power line network 26 in an access point 20 and a data input/output(“I/O”) device, such as a computer 51, as well known in the art, andfurthermore selectively controls the length of payload symbols includedin a PLC signal frame structure in accordance with the presentinvention. The inventive PLC transceiver 50 is described below ascontaining modules, which perform PLC signal processing using techniqueswell known in the prior art, and which are modified in accordance withthe present invention to perform PLC signal processing where a PLCsignal frame structure from which PLC signals are generated has aselected and controllable payload symbol length. See, for example, U.S.patent application Ser. No. 10/211,033, filed Aug. 2, 2002 and Ser. No.10/309,567, filed Dec. 4, 2002, each of which is assigned to theassignee of this application and incorporated by reference herein, for adescription of conventional PLC transceiver construction and operation.It is to be understood that the modules of the PLC transceiver 50described below as performing data or signal processing operationsconstitute a software module, a hardware module or a combinedhardware/software module. In addition, each of the modules suitablycontains a memory storage area, such as RAM, for storage of data andinstructions for performing processing operations in accordance with thepresent invention. Alternatively, instructions for performing processingoperations can be stored in hardware in one or more of the modules.

Referring to FIG. 2, the PLC transceiver 50 includes a central processorunit (“CPU”) 52 coupled to a data forward error correction (“FEC”)encoder 54 and a data FEC decoder 56. An OFDM modulator 58 couples theencoder 54 to an analog front end (“AFE”) 59, and an OFDM demodulator 60couples the AFE 59 to the decoder 56. The encoder 54 includes ascrambler module 62, a Reed-Solomon encoder module 64, a convolutionencoder module 68 and a bit interleaver module 70 connected to oneanother in the recited sequence. The decoder 56 includes ade-interleaver module 72, a de-puncture module 74, a viterbi decodermodule 76, a Reed Solomon decoder module 78 and a de-scrambler module 80connected to one another in the recited sequence. The modulator 58includes a mapper module 82, a reconfigurable inverse fast fourier(“IFFT”) processor module 84, a preamble module 86, a cyclic prefixmodule 88 and an RC shaping module 90 connected to one another in therecited sequence. The demodulator 60 includes a reconfigurable FFTprocessor module 82, a polar converter module 84 and a demodulatormodule 86 connected to one another in the recited sequence. In addition,a channel estimator 88 is coupled to the outputs of the polar convertermodule 84 and the FFT module 82, respectively, and a synchronizationdetector 91. The detector 91 also is coupled to the FFT module 82.

The modules 59, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88,90 and 91 are well known prior art PLC transceiver components that canperform prior art PLC signal processing operations which are also wellknown in the art. It is important to note that, in the prior art, all ofthe modules in the encoder 54 and the modulator 58 cannot bereprogrammed to process PLC signals based on different, selected payloadsymbol lengths. In other words, the encoder 54 and modulator 58 only canperform PLC signal processing operations in accordance with fixedpayload symbol length parameters, such that, for example, the mappermodule 82 and the IFFT module 84 cannot generate, for each payloadsymbol, different numbers of distinct PLC carriers for carryinginformation content. Similarly, all of the modules in the decoder 56 andthe modules 82, 84 and 86 in the demodulator 60 also cannot bereprogrammed to process received PLC signals based on different,selected payload symbol lengths.

In accordance with the present invention, the PLC transceiver 50 furtherincludes a symbol length controller (“SLC”) module 100 which is coupledto the CPU 52 and to each of modules contained in the encoder 54, thedecoder 56 and the modulator 58 and to the modules 82, 84 and 86 of thedemodulator 60. Furthermore, each of the modules in the encoder 54, themodulator 58 and the decoder 56, and the modules 82, 84 and 86 of thedemodulator 60 is reprogrammable and modifies its processing operationsbased on control parameter signals, which are associated with a payloadsymbol of a selected length and are supplied from the SLC module 100 ofthe inventive PLC transceiver 50. As discussed in further detail below,the SLC module 100 generates and transmits to the modules in the encoder54 and the modulator 58 control parameter signals, which are generatedbased on the payload symbol length selected for generating PLC signals.The control signals modify the processing operations that the modulesperform for generating PLC signals based on a PLC signal frame structurehaving payload symbols whose length is selected in accordance with thepresent invention. Further, the SLC module 100 generates and transmitsto the modules 82, 84 and 86 in the demodulator 60 and to each of themodules in the decoder 56 control parameter signals, which are generatedbased on the selected payload symbol length associated with received PLCsignals. The control signals modify the processing operations performedfor processing received PLC signals, such that information content databits are extracted from the received PLC signals in accordance with thelength selected for the payload symbols of the PLC signal framestructure from which the received PLC signals were generated.

For purpose of highlighting the inventive features, it is assumed thateach of the modules in the encoder 54, the modulator 58, the decoder 56and of the demodulator 60 normally operates in a default legacy PLCmode. In the legacy mode, PLC signal processing operations are performedin accordance with a legacy PLC signal frame structure design, whichrequires a fixed, predetermined length frame structure, a fixed,predetermined length payload portion and that the payload symbolscontained in the payload portion have a same fixed, predeterminedlength. The control signals supplied by the SLC module 100 modify theprocessing operations performed at (i) the encoder 54 and modulator 58to provide that a PLC signal frame structure having the payload symbollength identified in the control signal is generated, and (ii) thedemodulator 60 and decoder 56 to provide that a received PLC signal isprocessed in accordance with a PLC signal frame structure having thepayload symbol length identified in the control signals. For ease ofreference, the present invention is described in connection with anexemplary prior art PLC signal frame structure 120 shown in FIG. 3.Referring to FIG. 3, the frame structure 120 includes a payload portion122, which primarily contains information content, interposed between astart delimiter 124 and an end delimiter 126, both of which containoverhead data.

In a preferred embodiment, the SLC module 100 selects a payload symbollength and generates and transmits to the encoder 54 and the modulator58 control signals which provide that the overall length of the payloadportion of a PLC signal frame structure generated based on the selectedpayload symbol length is the same as the length of the legacy PLCpayload portion.

The operation of the PLC transceiver 50 is illustrated below withreference to the transmission of PLC signals from a source PLCtransceiver 50A (not shown), which is contained in the electronicappliance 21A that is coupled to the network 26 in the access point 20A,to a destination PLC transceiver 50D, which is contained in theelectronic appliance 21D that is coupled to a different point of thenetwork 26 in the access point 20A than the transceiver 50A, in the PLCsystem 10 as shown in FIG. 1. For ease of reference, the modules withinthe respective transceivers 50A and 50D are referred to below usingcorresponding alphabetical suffixes, e.g., the transceiver 50A includesthe SLC module 100A.

FIG. 4 shows an exemplary preferred process 200 that the source anddestination PLC transceivers 50A, 50D perform for generating PLC signalsbased on a PLC frame structure having a payload symbol length selectedbased on channel quality data and node configuration data. Based on thechannel quality data and the node configuration data, the SLC module100A preferably selects a length for the payload symbols that maximizesthe data throughput rate and also conforms to legacy requirementsconcerning the maximum length of the payload portion of the PLC framestructure.

Referring to FIG. 4, in step 202, the source PLC transceiver 50A, whichdesires to transmit information content to the destination PLCtransceiver 50D, initially generates PLC maintenance data signals in theROBO mode and transmits the maintenance PLC data signals onto thenetwork 26 for receipt by the destination PLC transceiver 50D. Theestimator module 88D, using well known prior art techniques, analyzesthe PLC signals transmitted by the transceiver 50A to determine channelquality in the segment of the network 26 of the PLC system 10 extendingbetween the transceivers 50A and 50D, and then routes the channelquality data to the CPU 52D. The CPU 52D, in turn, suitably providesthat the PLC transceiver 50D transmits the channel quality data onmaintenance PLC signals, over the network 26, for receipt at thetransceiver 50A. The transceiver 50A, using techniques well known in theart, extracts the channel quality data from the received PLC signal androutes the channel quality data, via the CPU 52A, to the SLC module100A. In a preferred embodiment, the SLC module 100A further includesnode configuration data that was supplied on PLC signals orpreprogrammed into the module 100A using suitable, well known

each payload symbol is 184 samples and the system clock is at 50 MHz,such that Ts is 8.4 μsec.

If the channel quality data is high, the SLC module 100A computes alength for the payload symbols that is greater than the length of thelegacy payload symbol. The increased length of a payload symbol withinthe fixed length payload portion of the legacy frame structuretranslates into a predetermined number of available PLC carriers thatcan be modulated with information content data and generated fortransmission, where the predetermined number is greater that the numberof PLC carriers that can be generated based on the legacy PLC symbollength. In preferred embodiments, the SLC module 100A provides that morethan the legacy number of PLC carriers are generated for a payloadsymbol as follows.

(1) The SLC module 100 decreases the bandwidth of each of the distinctavailable PLC carriers, such that a larger number of narrower bandwidthdistinct PLC carriers, evenly spaced across the legacy PLC spectrum, canbe generated. For example, in the legacy PLC system, 256 distinct PLCcarriers are evenly spaced across the legacy PLC spectrum, which forexample is between about 2 MHz and about 20 MHz. By narrowing thebandwidth of each of the 256 distinct PLC carriers by, for example,one-half, 512 distinct PLC carriers evenly spaced across the same 18 MHzlegacy spectrum can be generated for carrying the increased informationcontent data associated with an increased length payload symbol.

(2) The SLC module 100A provides that distinct PLC carriers aredistributed across a PLC frequency spectrum which is a wider than thelegacy PLC frequency spectrum. For example, the SLC module 100 increasesthe available PLC frequency spectrum from between about 2 MHz to about19 MHz (as in a legacy PLC system) to between about 2 MHz and about 25MHz. In this expanded PLC frequency spectrum, the SLC module 100Aprovides that distinct PLC carriers are evenly distributed across theexpanded PLC frequency spectrum, where the bandwidth of each of thedistinct PLC carriers is (a) the same as in the legacy PLC system or (b)narrower than in the legacy PLC system as described above in (1).

(3) The SLC module 100A resets the system clock to a higher frequency,such as 60 MHz, than the legacy PLC system clock frequency. The increasein the system clock frequency increases the sampling rate, which permitsthe range of the available PLC frequency spectrum to be increasedrelative to the legacy PLC system frequency spectrum. Thus, the SLCmodule 100A provides that more distinct PLC carriers can be generated,similarly as described in (2)(a) or (2)(b), for the longer payloadsymbol lengths.

Further in step 204, based on the selected increased symbol length, theSLC module 100A accordingly determines a corresponding NFFT, whichexceeds the NFFT for the PLC legacy system.

By increasing the payload symbol length while maintaining the legacypayload portion length unchanged, the payload portion includes fewersymbols than in the PLC legacy system. The increased length of a payloadsymbol, however, does not result in a proportional increase in thelength of the cyclic prefix for a payload symbol. The cyclic prefixlength for the increased length payload symbol is maintainedsubstantially the same as in the legacy system, because thecharacteristics of the PLC system are the same and because the highchannel quality permits a relatively short cyclic prefix length betweenconsecutive PLC signal transmissions corresponding to consecutivepayload symbols. Thus, the cyclic prefix in the increased length payloadsymbol occupies a smaller fraction of the length of the payload symbolthan the length that a cyclic prefix in the shorter, legacy lengthpayload symbol occupies. Consequently, the information content portionof the increased length payload symbols occupies a portion of the PLCframe structure that is greater than the portion of the legacy PLC framestructure occupied by information content contained in the shorter,legacy PLC length payload symbols, thereby increasing the datathroughput rate.

Referring to FIG. 6, which shows a payload portion of a fixed legacy PLCsystem length including increased length payload symbols, the SLC module100A in a preferred embodiment selects an increased payload symbollength corresponding to a NFFT of 2048 samples. Further, the SLC module100A, by evaluating the channel quality data and also based on the nodeconfiguration data, determines that N_CP needs to be 368 samples toprovide a sufficiently long cyclic prefix to avoid degradation based onintersymbol interference. Therefore, referring to Equation (1), for a 50MHz system clock, the length Ts_new of the new increased length payloadsymbol is 48 μsec and the payload portion includes 28 symbols. Theselected length provides that the total payload portion length (28symbols)(48 μsec/symbol) is the same as the legacy PLC system payloadportion length (160 symbols)(8.4 μsec/symbol). It is be understood thatthe SLC module 100A can suitably select the symbol length to have valuescorresponding to NFFT equal to 512, 1024, etc. samples.

Referring again to FIG. 4, in step 206 the SLC module 100A transmitscontrol parameter signals associated with the selected symbol length tothe modules within the encoder 54A to provide that the encoder 54Agroups the raw data into data blocks in accordance with the selectedsymbol length. In addition, the interleaver module 70A based on thecontrol signals, assigns a greater number of data bits for mapping intoa payload symbol, because an increased number of distinct PLC carrierscan be generated for the increased length payload symbol.

In step 208, the SLC module 100A transmits control signals, which aregenerated based on the channel quality data, the node configuration dataand known prior art tone maps and masks, to the mapper module 82A andthe IFFT module 84A to provide that processing operations are performedin accordance with the selected symbol length. For example, the controlsignals reprogram the IFFT module 84A to operate in a 2048 sample mode.

In step 210, the SLC module 100A transmits control signals to thepreamble module 86A which indicate the length of a cyclic prefix to beinserted in each payload symbol. Further in step 210, the SLC module100A transmits control signals to the RC shaper 90A to adjust filteringoperations, as suitable, based on either (i) the expanded PLC frequencyspectrum or (ii) the narrowing of the bandwidth of individual PLCcarriers within the PLC frequency spectrum, where the PLC frequencyspectrum is legacy sized or expanded.

In step 212, the PLC transceiver 50A transmits, over the network 26 forreceipt at the transceiver 50D, the PLC signals generated based on theselected payload symbol length within the legacy for the framestructure. It is further noted that the frame structure further includesframe control configuration data in the start delimiter. Theconfiguration data, which includes channel quality data and selectedpayload symbol length data, is transmitted on PLC signals to the PLCtransceiver 50D before the PLC signals containing information content,and corresponding to the payload symbols, are transmitted.

In step 214, the PLC transceiver 50D receives the PLC signalstransmitted from the PLC transceiver 50A. The demodulator and decodermodules 60D and 56D, using well known techniques in the art, demodulateand decode the overhead data transmitted in connection with the startand stop delimiter portions of the frame structure to extract theselected symbol length, and the associated frame control, channelquality and node configuration data included therein. The decoder module56D then routes the payload symbol length and the other associatedcontrol data to the CPU 52D, which in turn routes the symbol length andthe associated control data to the SLC module 100D. Based on the symbollength and the associated control data, the SLC module 100D generatesand transmits to the modules 82, 84 and 86 of the demodulator 60 and toeach of the modules of the decoder 56 suitable control parameter signalsto provide that demodulation and decoding of the received PLC signals isperformed based on the selected payload symbol length. For example, theFFT module 82 is reconfigured to perform a FFT processing at 2048samples, rather than at the default PLC legacy mode of 256 samples.Processing modifications analogous to those implemented at the mapperand the encoder module in the transceiver 50A are performed at thedemodulator module 86D and the modules of the decoder module 56D toprovide for proper demodulation and decoding based on the longer lengthpayload symbols.

It is known that some legacy PLC frame structures have a design thatprecludes the introduction of data indicating a particular symbol lengthbased upon which PLC signal processing should be performed at adestination PLC transceiver. In these circumstances, the source PLCtransceiver 50 includes symbol length information in a higher protocollayer, such as the IP layer, associated with a PLC signal transmission.Alternatively, the source PLC transceiver includes symbol lengthinformation in a PLC maintenance signal transmission routinelytransmitted to the destination PLC transceiver, as well known in theart. The PLC destination transceiver suitably extracts the symbol lengthinformation from the maintenance PLC signal.

In a further preferred embodiment, the CPU 52 in the PLC transceiver 50controls exchanges of maintenance signals with other PLC transceivers inthe PLC system and, based on the exchanges, determines whether the otherPLC transceivers have the processing capability to select payload symbollength. The CPU 52 generates a table representative of the PLC signaltransmission capabilities of the respective PLC transceivers and causesthe information contained in the table to be transmitted on maintenancePLC signals over the PLC system for receipt by other PLC transceivershaving the capability to process PLC signals based on a select payloadsymbol length.

In a preferred embodiment, the CPU 52 in a source PLC transceivertransmits to a destination PLC transceiver maintenance PLC signalsidentifying the length of payload symbols to be included in subsequentPLC signal transmissions from the source PLC transceiver. In a furtherpreferred embodiment, a destination PLC transceiver transmitsmaintenance signals to the source PLC transceiver acknowledging receiptof the symbol length information provided by the source PLC transceiverand accordingly processes PLC signals received from the source PLCtransceiver at the selected payload symbol length.

Although preferred embodiments of the present invention have beendescribed and illustrated, it will be apparent to those skilled in theart that various modifications may be made without departing from theprinciples of the invention.

1. A method for transferring data on power line communications (“PLC”)signals over a PLC system, wherein the PLC system operates in accordancewith a PLC signal frame structure including a payload portion andwherein the payload portion has a predetermined, fixed length andincludes at least one payload symbol, the method comprising: obtainingchannel quality data for a PLC system signal path extending between asource PLC transceiver and a destination PLC transceiver; computing,based on at least one of the channel quality data and node configurationdata, a payload symbol length; generating a payload portion including atleast one payload symbol of the computed length, wherein the length orsum of the lengths of the at least one payload symbol contained in thegenerated payload portion equals the predetermined length of the payloadportion; and modifying processing operations at the source PLCtransceiver for generating PLC carriers in accordance with the PLCsignal frame structure including the at least one payload symbol havingthe computed payload length.
 2. The method of claim 1 furthercomprising: modifying processing operations at the destination PLCtransceiver for extracting data from the PLC signal frame structurebased on the computed length payload symbol.
 3. The method of claim 1,wherein the source PLC transceiver operates in a default mode forgenerating PLC carriers based on a PLC signal frame structure includingpayload symbols having a first length, wherein the computed payloadsymbol length exceeds the first length, thereby increasing PLC datathroughput rate and efficiency of utilization of the PLC system as achannel for transferring communications data.
 4. The method of claim 1,wherein the destination PLC transceiver operates in a default mode forextracting information content from a received PLC signal generatedbased on a PLC frame structure including payload symbols having a firstlength, wherein the computed payload symbol length exceeds the firstlength.
 5. The method of claim 1 further comprising: transmitting fromthe PLC source transceiver, over the PLC system and for receipt at thedestination PLC transceiver, PLC carriers generated in accordance withthe frame structure; determining at the destination PLC transceiver,from the PLC carriers transmitted from the source PLC transceiver,whether the payload symbols used to generate the received PLC carriershave a length other than a default mode payload symbol length; and atthe destination PLC transceiver, extracting information content datafrom the received PLC carriers based on the payload lengthdetermination.
 6. The method of claim 3 further comprising: generating apredetermined number of distinct PLC carriers based on the computedpayload symbol length, wherein the predetermined number of PLC carriersexceeds an available number of distinct PLC carriers generated duringoperation of the source PLC transceiver in the default mode.
 7. Themethod of claim 6, wherein the predetermined number of distinct PLCcarriers have a narrower bandwidth than the bandwidth of the PLCcarriers generated during operation of the source PLC transceiver in thedefault mode.
 8. The method of claim 6, wherein the predetermined numberof distinct frequency PLC carriers are distributed across a PLCfrequency spectrum broader than a PLC frequency spectrum required by thedefault mode.
 9. The method of claim 3 further comprising: increasing asampling rate of a clock included in the source PLC transceiver to arate exceeding a sampling rate associated with the default mode.
 10. Themethod of claim 8, wherein the predetermined number of distinct PLCcarriers has a narrower bandwidth than the bandwidth of the PLC carriersgenerated during operation of the source PLC transceiver in the defaultmode.
 11. The method of claim 9, wherein the predetermined number ofdistinct PLC carriers has a narrower bandwidth than the bandwidth of thePLC carriers generated during operation of the source PLC transceiver inthe default mode.
 12. The method of claim 1, wherein the source PLCtransceiver operates in a default mode for generating PLC carriers basedon a PLC signal frame structure including payload symbols having a firstlength, wherein the computed payload symbol length is less than thefirst length.
 13. The method of claim 1, wherein the PLC system includespower and communications data distribution components operating inaccordance with at least one operating mode.
 14. The method of claim 1,wherein the at least one operating mode includes PLC system operation inaccordance with processing capabilities at a range of processing speeds.15. The method of claim 1, wherein the PLC carriers have frequencieswithin a PLC frequency spectrum extending between about 2 MHz and about30 MHz.
 16. A power line communications (“PLC”) transceiver fortransferring, over a PLC system, PLC signals generated in accordancewith a PLC signal frame structure including a payload portion, whereinthe payload portion has a predetermined, fixed length and includes atleast one payload symbol, the PLC transceiver comprising: a channelestimator for obtaining channel quality data for a PLC system signalpath extending to a destination PLC transceiver; a symbol lengthcontroller coupled to the channel estimator and for computing, based onat least one of the channel quality data and node configuration datastored in the symbol length controller, a payload symbol length, whereinthe computed payload symbol length is used for generating a payloadportion including at least one payload symbol of the computed length,wherein the length or sum of the lengths of the at least one payloadsymbol contained in the generated payload portion equals thepredetermined length of the payload portion; and a PLC carrier generatorcoupled to the symbol length controller for generating PLC carrierscontaining information content, wherein the symbol length controllersupplies the PLC signal generator with control signals for modifyingprocessing operations in accordance with a PLC signal frame includingthe at least one payload symbol having the computed symbol length. 17.The PLC transceiver of claim 16, wherein the PLC carrier generatornormally operates in a default mode, wherein in the default mode apayload symbol has a predetermined length.
 18. The PLC transceiver ofclaim 17, wherein the computed payload symbol length exceeds or is lessthan the predetermined payload symbol length for the default mode. 19.The PLC transceiver of claim 16, wherein the PLC carrier generatorfurther comprises a reprogrammable forward error correction (“FEC”)encoder and a reprogrammable FEC decoder capable of being programmed toperform PLC processing on data blocks containing information contentdata in accordance with a selected payload symbol length, wherein thedata blocks are selected from at least one of a predetermined number ofsizes.
 20. The PLC transceiver of claim 16, wherein the PLC carriergenerator further comprises a reprogrammable interleaver module and areprogrammable deinterleaver module which are coupled respectively tothe FEC encoder and FED decoder, wherein each of the interleaver anddeinterleaver modules is capable of being programmed to perform PLCsignal processing on data blocks containing information content data inaccordance with a selected payload symbol length.
 21. The PLCtransceiver of claim 16 further comprising: a computer processing unit(“CPU”) coupled to the symbol length controller and the PLC carriergenerator, wherein the CPU controls Phy layer software operations andperforms channel quality assessment operations.